Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1135 AM EDT Mon Jul 02 2018
Valid 12Z Thu Jul 05 2018 - 12Z Mon Jul 09 2018
...Overview and weather threats/highlights...
A closed upper high will settle into the Rockies/Four Corners
region by late this week and weekend as upper troughing over
Canada dips into New England. This evolution will bring a warming
trend to a majority of the West into northern Plains (some
readings 10F or more above normal) and cooler temperatures (back
near average) to the East. Even with the episode of upper
troughing over the eastern U.S., expect above average heights
aloft over nearly the entire lower 48. Precipitation will
generally focus around the periphery of the upper high. The most
agreeable signal for highest 5-day rainfall totals exists near the
central Gulf Coast where a retrograding upper level inverted
trough/low and possible weak surface reflection may enhance
activity. Clouds/rainfall will tend to keep temperatures near to
just below average over the Gulf Coast region. A front
progressing from the Great Lakes-central Plains into the
East/South will bring a period of showers/thunderstorms with some
locally heavy rainfall. Another frontal system/upper shortwave
progressing through the Northwest into the northern Plains should
bring mostly light/scattered precipitation to the
Northwest/northern Rockies and then showers/storms to the northern
Plains-upper MS Valley.
...Guidance evaluation/preferences...
The updated forecast reflected little meaningful change from
previous issuance. There is still sufficient agreement for
significant features in principle to favor an operational model
blend days 3-5 Thu-Sat followed by a model/ensemble mean blend to
account for typical increase in forecast uncertainty at extended
time frames. Detail issues of note: 00Z/06Z GFS runs become
faster and more sheared than most other guidance for the upper
feature that retrogrades along the Gulf Coast, with the model
blend providing 70 percent weight of the non-GFS scenario.
Individual model runs and ensemble spaghetti plots suggest
increasing shortwave detail uncertainty (without well-defined
clustering among ensemble systems) over the northeastern
Pacific/western North America by days 6-7 Sun-Mon. This spread
tempers confidence a bit for details of the northern Plains front
late in the forecast.
Rausch/Fracasso
WPC medium range forecasts of 500 mb heights, surface systems,
weather grids, quantitative precipitation, and winter weather
outlook probabilities are found at:
http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4